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Published on: July 19, 2019
Excited-State Intramolecular Proton Transfer and Global Aromaticity
Naoko Nishina1, Toshiki Mutai2, Jun-Ichi Aihara1
1Department of Chemistry, Faculty of Science, Shizuoka University , Oya, Shizuoka 422-8529, Japan.
Global aromaticity influences excited-state intramolecular proton transfer (ESIPT) reactions. Enhanced aromaticity in the tautomeric product generally facilitates ESIPT, while decreased aromaticity can create an energy barrier, impacting reaction feasibility.
Area of Science:
- Physical Chemistry
- Theoretical Chemistry
- Photochemistry
Background:
- Excited-state intramolecular proton transfer (ESIPT) is a crucial photochemical process.
- Understanding the factors governing ESIPT is essential for controlling photochemical reactions.
- Aromaticity plays a role in chemical stability and reactivity.
Purpose of the Study:
- To investigate the influence of global aromaticity on ESIPT processes.
- To determine the relationship between aromaticity changes and ESIPT reaction barriers.
- To assess the role of excited-state aromaticity in ESIPT feasibility.
Main Methods:
- General survey of various ESIPT processes.
- Analysis of topological resonance energy (TRE) for reactants and tautomeric products in excited states.
- Evaluation of aromaticity changes during the ESIPT reaction pathway.
Main Results:
- Most studied ESIPT processes showed increased TRE in the tautomeric product compared to the reactant in the excited state.
- A significant decrease in aromaticity for the transient tautomer in the excited state leads to an energy barrier for the reaction.
- Excited-state aromaticity is a key, though not exclusive, determinant of ESIPT allowance.
Conclusions:
- Global aromaticity is a critical factor influencing the energetics and feasibility of ESIPT reactions.
- The change in aromaticity between the reactant and the excited-state tautomer dictates the energy landscape of ESIPT.
- Understanding excited-state aromaticity provides insights into controlling and predicting ESIPT pathways.
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